Compressed air systems are commonly installed on heavy duty vehicles to operate the brakes of the vehicle and other air actuated appliances. It has become increasing common to install an air dryer in such systems to remove the moisture entrained in the compressed air, as moisture can cause system components to freeze and become inoperative during cold weather operation and also because moisture severely reduces the life of many system components. Although the present invention is primarily intended for use with automotive air brake systems, it can also be used with stationary systems, such as those used with industrial machinery, etc.
Common air dryers used in compressed air systems include a desiccant material which removes the moisture entrained in the compressed air. The desiccant must be regenerated or purged periodically by reverse flowing a segregated portion of compressed air through the desiccant to remove the moisture. However, common desiccants may only be used for a limited time, which varies accordingly to a number of factors, including the degree of saturation of the air which has passed through the desiccant and the number of times the desiccant has been purged. Currently, desiccants are replaced at regular intervals. This means that the desiccant is changed more often than necessary in some systems, while in other systems the desiccant should have been replaced earlier.